docs: def get_urls(self):
          """
          Add a preview URL.
          """
          from django.conf.urls import patterns, url
          urls = super(RecurrenceRuleAdmin, self).get_urls()
          my_urls = patterns(
              '',
              url(
                  r'^preview/$',
                  self.admin_site.admin_view(self.preview),
                  name='icekit_events_recurrencerule_preview'
              ),
          )
          return my_urls + urls